Pdc bits having rolling cutters and using mixed chamfers

ABSTRACT

A cutting tool cutting tool may include a tool body having a plurality of blades extending radially therefrom, a plurality of rotatable cutting elements having a first chamfer mounted on at least one of the plurality of blades, and a plurality of non-rotatable cutting elements having a second, distinct chamfer mounted on at least one the plurality of blades.

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. §119, this application claims the benefit of U.S.Provisional Application No. 61/783,428, filed on Mar. 14, 2013, and U.S.Provisional Application No. 61/721,908, filed on Nov. 2, 2012, both ofwhich are incorporated by reference in their entirety.

BACKGROUND

Drill bits used to drill wellbores through earth formations generallyare made within one of two broad categories of bit structures. Drillbits in the first category are generally known as “roller cone” bits,which include a bit body having one or more roller cones rotatablymounted to the bit body. The bit body is typically formed from steel oranother high strength material. The roller cones are also typicallyformed from steel or other high strength material and include aplurality of cutting elements disposed at selected positions about thecones. The cutting elements may be formed from the same base material asis the cone. These bits are typically referred to as “milled tooth”bits. Other roller cone bits include “insert” cutting elements that arepress (interference) fit into holes formed and/or machined into theroller cones. The inserts may be formed from, for example, tungstencarbide, natural or synthetic diamond, boron nitride, or any one orcombination of hard or superhard materials.

Drill bits of the second category are typically referred to as “fixedcutter” or “drag” bits. This category of bits has no moving elements butrather have a bit body formed from steel or another high strengthmaterial and cutters (sometimes referred to as cutter elements, cuttingelements or inserts) attached at selected positions to the bit body. Forexample, the cutters may be formed having a substrate or support studmade of carbide, for example tungsten carbide, and an ultra hard cuttingsurface layer or “table” made of a polycrystalline diamond material or apolycrystalline boron nitride material deposited onto or otherwisebonded to the substrate at an interface surface.

An example of a prior art drag bit having a plurality of cutters withultra hard working surfaces is shown in FIG. 1A. A drill bit 10 includesa bit body 12 and a plurality of blades 14 that are formed on the bitbody 12. The blades 14 are separated by channels or gaps 16 that enabledrilling fluid to flow between and both clean and cool the blades 14 andcutters 18. Cutters 18 are held in the blades 14 at predeterminedangular orientations and radial locations to present working surfaces 20with a desired backrake angle against a formation to be drilled.Typically, the working surfaces 20 are generally perpendicular to theaxis 19 and side surface 21 of a cylindrical cutter 18. Thus, theworking surface 20 and the side surface 21 meet or intersect to form acircumferential cutting edge 22.

Nozzles 23 are typically formed in the drill bit body 12 and positionedin the gaps 16 so that fluid can be pumped to discharge drilling fluidin selected directions and at selected rates of flow between the cuttingblades 14 for lubricating and cooling the drill bit 10, the blades 14,and the cutters 18. The drilling fluid also cleans and removes thecuttings as the drill bit rotates and penetrates the geologicalformation. The gaps 16, which may be referred to as “fluid courses,” arepositioned to provide additional flow channels for drilling fluid and toprovide a passage for formation cuttings to travel past the drill bit 10toward the surface of a wellbore (not shown).

The drill bit 10 includes a shank 24 and a crown 26. Shank 24 istypically formed of steel or a matrix material and includes a threadedpin 28 for attachment to a drill string. Crown 26 has a cutting face 30and outer side surface 32. The particular materials used to form drillbit bodies are selected to provide adequate toughness, while providinggood resistance to abrasive and erosive wear. For example, in the casewhere an ultra hard cutter is to be used, the bit body 12 may be madefrom powdered tungsten carbide (WC) infiltrated with a binder alloywithin a suitable mold form. In one manufacturing process the crown 26includes a plurality of holes or pockets 34 that are sized and shaped toreceive a corresponding plurality of cutters 18.

The combined plurality of surfaces 20 of the cutters 18 effectivelyforms the cutting face of the drill bit 10. Once the crown 26 is formed,the cutters 18 are positioned in the pockets 34 and affixed by anysuitable method, such as brazing, adhesive, mechanical means such asinterference fit, or the like. The design depicted provides the pockets34 inclined with respect to the surface of the crown 26. The pockets 34are inclined such that cutters 18 are oriented with the working face 20at a desired rake angle in the direction of rotation of the bit 10, soas to enhance cutting. It should be understood that in an alternativeconstruction (not shown), the cutters may each be substantiallyperpendicular to the surface of the crown, while an ultra hard surfaceis affixed to a substrate at an angle on a cutter body or a stud so thata desired rake angle is achieved at the working surface.

A typical cutter 18 is shown in FIG. 1B. The typical cutter 18 has acylindrical cemented carbide substrate body 38 having an end face orupper surface 54 referred to herein as the “interface surface” 54. Anultra hard material layer (cutting layer) 44, such as polycrystallinediamond or polycrystalline cubic boron nitride layer, forms the workingsurface 20 and the cutting edge 22. A bottom surface 52 of the ultrahard material layer 44 is bonded on to the upper surface 54 of thesubstrate 38. The bottom surface 52 and the upper surface 54 are hereincollectively referred to as the interface 46. The top exposed surface orworking surface 20 of the cutting layer 44 is opposite the bottomsurface 52. The cutting layer 44 typically has a flat or planar workingsurface 20, but may also have a curved exposed surface, that meets theside surface 21 at a cutting edge 22.

Generally speaking, the process for making a cutter 18 employs a body oftungsten carbide as the substrate 38. The carbide body is placedadjacent to a layer of ultra hard material particles such as diamond orcubic boron nitride particles and the combination is subjected to hightemperature at a pressure where the ultra hard material particles arethermodynamically stable. This results in recrystallization andformation of a polycrystalline ultra hard material layer, such as apolycrystalline diamond or polycrystalline cubic boron nitride layer,directly onto the upper surface 54 of the cemented tungsten carbidesubstrate 38.

One type of ultra hard working surface 20 for fixed cutter drill bits isformed as described above with polycrystalline diamond on the substrateof tungsten carbide, typically known as a polycrystalline diamondcompact (PDC), PDC cutters, PDC cutting elements, or PDC inserts. Drillbits made using such PDC cutters 18 are known generally as PDC bits.While the cutter or cutter insert 18 is typically formed using acylindrical tungsten carbide “blank” or substrate 38 which issufficiently long to act as a mounting stud 40, the substrate 38 mayalso be an intermediate layer bonded at another interface to anothermetallic mounting stud 40.

The ultra hard working surface 20 is formed of the polycrystallinediamond material, in the form of a cutting layer 44 (sometimes referredto as a “table”) bonded to the substrate 38 at an interface 46. The topof the ultra hard layer 44 provides a working surface 20 and the bottomof the ultra hard layer cutting layer 44 is affixed to the tungstencarbide substrate 38 at the interface 46. The substrate 38 or stud 40 isbrazed or otherwise bonded in a selected position on the crown of thedrill bit body 12 (Figure la). As discussed above with reference to FIG.1 a, the PDC cutters 18 are typically held and brazed into pockets 34formed in the drill bit body at predetermined positions for the purposeof receiving the cutters 18 and presenting them to the geologicalformation at a rake angle.

Bits 10 using conventional PDC cutters 18 are sometimes unable tosustain a sufficiently low wear rate at the cutter temperaturesgenerally encountered while drilling in abrasive and hard rock. Thesetemperatures may affect the life of the bit 10, especially when thetemperatures reach 700-750° C., resulting in structural failure of theultra hard layer 44 or PDC cutting layer. A PDC cutting layer includesindividual diamond “crystals” that are interconnected. The individualdiamond crystals thus form a lattice structure. A metal catalyst, suchas cobalt may be used to promote recrystallization of the diamondparticles and formation of the lattice structure. Thus, cobalt particlesare typically found within the interstitial spaces in the diamondlattice structure. Cobalt has a significantly different coefficient ofthermal expansion as compared to diamond. Therefore, upon heating of adiamond table, the cobalt and the diamond lattice will expand atdifferent rates, causing cracks to form in the lattice structure andresulting in deterioration of the diamond table.

It has been found by applicants that many cutters 18 develop cracking,spalling, chipping and partial fracturing of the ultra hard materialcutting layer 44 at a region of cutting layer subjected to the highestloading during drilling. This region is referred to herein as the“critical region” 56. The critical region 56 encompasses the portion ofthe ultra hard material layer 44 that makes contact with the earthformations during drilling. The critical region 56 is subjected to highmagnitude stresses from dynamic normal loading, and shear loadingsimposed on the ultra hard material layer 44 during drilling. Because thecutters are typically inserted into a drag bit at a rake angle, thecritical region includes a portion of the ultra hard material layer nearand including a portion of the layer's circumferential edge 22 thatmakes contact with the earth formations during drilling.

The high magnitude stresses at the critical region 56 alone or incombination with other factors, such as residual thermal stresses, canresult in the initiation and growth of cracks 58 across the ultra hardlayer 44 of the cutter 18. Cracks of sufficient length may cause theseparation of a sufficiently large piece of ultra hard material,rendering the cutter 18 ineffective or resulting in the failure of thecutter 18. When this happens, drilling operations may have to be ceasedto allow for recovery of the drag bit and replacement of the ineffectiveor failed cutter. The high stresses, particularly shear stresses, mayalso result in delamination of the ultra hard layer 44 at the interface46.

In some drag bits, PDC cutters 18 are fixed onto the surface of the bit10 such that a common cutting surface contacts the formation duringdrilling. Over time and/or when drilling certain hard but notnecessarily highly abrasive rock formations, the edge 22 of the workingsurface 20 that constantly contacts the formation begins to wear down,forming a local wear flat, or an area worn disproportionately to theremainder of the cutting element. Local wear flats may result in longerdrilling times due to a reduced ability of the drill bit to effectivelypenetrate the work material and a loss of rate of penetration caused bydulling of edge of the cutting element. That is, the worn PDC cutteracts as a friction bearing surface that generates heat, whichaccelerates the wear of the PDC cutter and slows the penetration rate ofthe drill. Such flat surfaces effectively stop or severely reduce therate of formation cutting because the conventional PDC cutters are notable to adequately engage and efficiently remove the formation materialfrom the area of contact. Additionally, the cutters are typically underconstant thermal and mechanical load. As a result, heat builds up alongthe cutting surface, and results in cutting element fracture. When acutting element breaks, the drilling operation may sustain a loss ofrate of penetration, and additional damage to other cutting elements,should the broken cutting element contact a second cutting element.

Additionally, another factor in determining the longevity of PDC cuttersis the generation of heat at the cutter contact point, specifically atthe exposed part of the PDC layer caused by friction between the PCD andthe work material. This heat causes thermal damage to the PCD in theform of cracks which lead to spalling of the polycrystalline diamondlayer, delamination between the polycrystalline diamond and substrate,and back conversion of the diamond to graphite causing rapid abrasivewear. The thermal operating range of conventional PDC cutters istypically 750° C. or less.

In U.S. Pat. No. 4,553,615, a rotatable cutting element for a drag bitwas disclosed with an objective of increasing the lifespan of thecutting elements and allowing for increased wear and cuttings removal.The rotatable cutting elements disclosed in the '615 patent include athin layer of an agglomerate of diamond particles on a carbide backinglayer having a carbide spindle, which may be journalled in a bore in abit, optionally through an annular bush. With significant increases inloads and rates of penetration, the cutting element of the '615 patentis likely to fail by one of several failure modes. Firstly, thin layerof diamond is prone to chipping and fast wearing. Secondly, geometry ofthe cutting element would likely be unable to withstand heavy loads,resulting in fracture of the element along the carbide spindle. Thirdly,the retention of the rotatable portion is weak and may cause therotatable portion to fall out during drilling. Fourthly, the prior artdoes not disclose optimization of the location of rotatable cuttingelements on a bit body.

Accordingly, there exists a continuing need for cutting elements thatmay stay cool and avoid the generation of local wear flats, and theincorporation of those cutting elements on a drill bit or other cuttingtool.

SUMMARY

This summary is provided to introduce a selection of concepts that arefurther described below in the detailed description. This summary is notintended to identify key or essential features of the claimed subjectmatter, nor is it intended to be used as an aid in limiting the scope ofthe claimed subject matter.

In one aspect, embodiments disclosed herein relate to a cutting toolthat includes a tool body having a plurality of blades extendingradially therefrom, a plurality of rotatable cutting elements having afirst chamfer mounted on at least one of the plurality of blades, and aplurality of non-rotatable cutting elements having a second, distinctchamfer mounted on at least one of the plurality of blades.

In another aspect, embodiments disclosed herein relate to a cutting toolthat includes a tool body having a plurality of blades extendingradially therefrom; a plurality of rotatable cutting elements, whereinthe plurality of rotatable cutting elements have at least two differingchamfer sizes based on their positioning along the plurality of blades

Other aspects and advantages of the invention will be apparent from thefollowing description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A shows a perspective view of a conventional fixed cutter bit.

FIG. 1B shows a perspective view of a conventional PDC cutter.

FIG. 2 shows the progression of a wear flat in a conventional cuttingelement.

FIGS. 3A-B show profile views of a drill bit according to embodimentsdisclosed herein.

FIG. 4 shows a rotated profile view of a drill bit according toembodiments disclosed herein.

FIGS. 5A-B show an example small chamfer for use in an embodimentdisclosed herein.

FIGS. 6-8 show an example large chamfer for use in an embodimentdisclosed herein.

FIG. 9 shows the cutting force acting on two bevel sizes.

FIG. 10 shows the side force acting on two bevel sizes.

FIG. 11 shows a bit profile according to one embodiment disclosedherein.

FIG. 12 shows an exploded view of a cutting element assembly accordingto embodiments of the present disclosure.

FIG. 13 shows a cross-sectional view of a cutting element assemblyaccording to embodiments of the present disclosure.

DETAILED DESCRIPTION

In one or more aspects, embodiments disclosed herein relate to downholetools (including fixed cutter drill bits) using rotatable cuttingstructures. In one or more aspect, embodiments disclosed herein relateto downhole tools (including fixed cutter drill bits) using rotatablecutting structures in conjunction with conventional fixed cutters.Specifically, embodiments disclosed herein relate to improving the lifeof a drill bit (or other downhole tool) by positioning rotatable cuttingelements in particular arrangements on the drill bit.

Generally, rotatable cutting elements (also referred to as rollingcutters) described herein allow at least one surface or portion of thecutting element to rotate as the cutting elements contact a formation.As the cutting element contacts the formation, the cutting action mayallow portion of the cutting element to rotate around a cutting elementaxis extending through the cutting element. Rotation of a portion of thecutting structure may allow for a cutting surface to cut the formationusing the entire outer edge of the cutting surface, rather than the samesection of the outer edge, as observed in a conventional cuttingelement. The following discussion describes various embodiments for arotatable cutting element; however, the present disclosure is not solimited. One skilled in the art would appreciate that any cuttingelement capable of rotating may be used with the drill bit or othercutting tool of the present disclosure.

The rotation of the inner rotatable cutting element may be controlled bythe side cutting force and the frictional force between the bearingsurfaces. If the side cutting force generates a torque which canovercome the torque from the frictional force, the rotatable portionwill have rotating motion. The side cutting force may be affected bycutter side rake, back rake and geometry, including the working surfacepatterns disclosed herein. Additionally, the side cutting force may beaffected by the surface finishing of the surfaces of the cutting elementcomponents, the frictional properties of the formation, as well asdrilling parameters, such as depth of cut. The frictional force at thebearing surfaces may affected, for example, by surface finishing, mudintrusion, etc. The design of the rotatable cutters disclosed herein maybe selected to ensure that the side cutting force overcomes thefrictional force to allow for rotation of the rotatable portion. Variousdesign considerations of the present disclosure are described below, aswell as exemplary embodiments of rolling cutters.

Placement of Rolling Cutters

According to embodiments of the present disclosure, a bit designconsideration may include placement of rolling cutters on a drill bit.Placement design of rolling cutters on a drill bit may involve, first,predicting where conventional cutter (fixed cutter) wear occurs mostfrequently or quickly on a drill bit. For example, fixed cutter wear maybe predicted using engineering and design software, such as I-DEAS,“Integrated Design and Engineering Analysis Software”, or CAD software.Such engineering and design software may also be used to optimize bitstabilization dynamics using various placements of rolling cutters.Fixed cutter wear may also be predicted by observing and/or measuringwear flat sizes on dull drill bits. In particular, as a drill bit havingconventional, fixed cutters contacts and cuts an earthen formation, thecutting surface and cutting edge of a fixed cutter may wear and form awear flat. An example of a wear flat 2305 progression in a fixed cutter2300 is shown in FIG. 2.

Once fixed cutter wear is predicted, criteria for the placement ofrolling cutters may be set according to where the fixed cutter wearoccurs. For example, according to embodiments of the present disclosure,rolling cutter placement design may include replacing fixed cuttershaving the most amount of wear with rolling cutters. In one embodiment,rolling cutter placement design may include replacing half of the totalnumber of fixed cutters experiencing the largest amount of wear withrolling cutters. Further, in other embodiments, rolling cutter placementdesign may include replacing fixed cutters with rolling cutters on onlycertain blades of a drill bit.

According to embodiments of the present disclosure, rolling cutterplacement design criteria may be set so that rolling cutters and fixedcutters on a drill bit have a plural set configuration. Drill bitshaving a plural set configuration have more than one cutting element atat least one radial position with respect to the bit axis. Expressedalternatively, at least one cutting element includes a “back up” cuttingelement disposed at about the same radial position with respect to thebit axis. For example, referring to FIGS. 3A and 3B, a face side profileview of a drill bit 2400 having a plurality of cutting blades 2410 areshown, wherein the bits rotate in direction R. Primary blades 2410 aextend radially from substantially proximal the longitudinal axis A ofthe bit toward the periphery of the bit. Secondary blades 2410 b do notextend from substantially proximal the bit axis A, but instead extendradially from a location that is a distance away from the bit axis A.Cutting elements 2420, 2430 are positioned at the leading side of blades2410, wherein the leading sides of blades 2410 face in the direction ofbit rotation R and trailing sides of blades face the opposite direction.Further, as shown, cutting element 2420 trails cutting element 2430 inplural set configuration, i.e., cutting element 2420 “backs up” cuttingelement 2430 at about the same radial position with respect to the bitaxis A. Either cutting element 2420 or cutting element 2430, or bothcutting elements 2420 and 2430, may be rolling cutters. In a particularembodiment, a bit having a plural set cutter configuration may have atleast one trailing or backup cutting element that is rotatable (arolling cutter) and at least one leading or primary cutting element thatis a fixed cutter. In another embodiment, a bit having a plural setconfiguration may have at least one fixed cutter trailing cuttingelement and at least one rolling cutter leading cutting element.Advantageously, by using a plural set configuration having at least onerolling cutter, the cutting structure may be more robust.

Further, a bit may have a single set configuration of cutting elements,wherein each cutting element in a single set configuration is at aunique radial position of the bit. In embodiments having a single setconfiguration, a plurality of rolling cutters may be placed at variousunique radial positions with respect to the bit axis. For example, aplurality of rolling cutters may have a forward spiral or a reversespiral single set configuration, wherein the rolling cutters are placedin areas experiencing wear. As used herein, a forward spiral layoutrefers to a cutter placement where cutters having incrementallyincreasing radial distances from the bit centerline are placed in aclockwise distribution whereas a reverse spiral layout refers to acutter placement where cutters having incrementally increasing radialdistances from a bit centerline are placed in a counterclockwisedistribution. In some embodiments, the cutters may be placed in aforward spiral, where rotatable cutters are at least placed in the noseand/or shoulder region, are placed in the nose, shoulder, and gageregions in particular embodiments, and are placed in the cone, nose,shoulder, and gage regions in more particular embodiments. In someembodiments, the cutters may be placed in a reverse spiral, whererotatable cutters are at least placed in the nose and/or shoulderregion, are placed in the nose, shoulder, and gage regions in particularembodiments, and are placed in the cone, nose, shoulder, and gageregions in more particular embodiments.

Additionally, leading and trailing cutting elements may be placed on asingle blade.

However, as used herein, the term “backup cutting element” is used todescribe a cutting element that trails any other cutting element on thesame blade when the bit is rotated in the cutting direction. Further, asused herein, the term “primary cutting element” is used to describe acutting element provided on the leading edge of a blade. In other words,when a bit is rotated about its central longitudinal axis in the cuttingdirection, a “primary cutting element” does not trail any other cuttingelements on the same blade. Suitably, each primary cutting elements andoptional backup cutting element may have any suitable size and geometry.Primary cutting elements and backup cutting elements may have anysuitable location and orientation and may be rolling cutters or fixedcutters. In an example embodiment, backup cutting elements may belocated at the same radial position as the primary cutting element ittrails, or backup cutting elements may be offset from the primarycutting element it trails, or combinations thereof may be used.

In particular, each blade on a bit face (e.g., primary blades andsecondary blades) provides a cutter-supporting surface to which cuttingelements are mounted. Primary cutting elements may be disposed on thecutter-supporting surface of the blades and one or more of the primaryblades may also have backup cutting elements disposed on thecutter-supporting surface of the bit. In an exemplary embodiment, backupcutting elements may be provided on the cutter-supporting surface of oneor more of the bit primary blades in the cone region. In a differentexample embodiment, backup cutting elements may be provided on thecutter-supporting surface of any one or more secondary blades in theshoulder and/or gage region. In another example embodiment, backupcutting elements may be provided on the cutter-supporting surface of anyone or more primary blades in the gage region. In yet another exampleembodiment, the primary and/or secondary blades may have at least tworows of backup cutting elements disposed on the cutter-supportingsurfaces.

Primary cutting elements may be placed adjacent one another generally ina first row extending radially along each primary blade of a bit andalong each secondary blade of a bit. Further, backup cutting elementsmay be placed adjacent one another generally in a second row extendingradially along each primary blade in the shoulder region. Suitably, thebackup cutting elements form a second row that may extend along eachprimary blade in the shoulder region, cone region and/or gage region.Backup cutting elements may be placed behind the primary cuttingelements on the same primary blade, wherein backup cutting elementstrail the primary cutting elements on the same primary blades.

In general, primary cutting elements as well as backup cutting elementsneed not be positioned in rows, but may be mounted in other suitablearrangements provided each cutting element is either in a leadingposition (e.g., primary cutting element) or a trailing position (e.g.,backup cutting element). Examples of suitable arrangements may includewithout limitation, rows, arrays or organized patterns, randomly,sinusoidal pattern, or combinations thereof. Further, in otherembodiments, additional rows of cutting elements may be provided on aprimary blade, secondary blade, or combinations thereof.

In some embodiments of the present disclosure, rolling cutter placementdesign criteria may be set so that rolling cutters are positioned in theareas of the bit experiencing the greatest wear. For example, rollingcutters may be placed in the shoulder region of a drill bit. Referringto FIG. 4, a profile 39 of a bit 10 is shown as it would appear with allblades and all cutting elements (including primary cutting elements andback up cutting elements) rotated into a single rotated profile. A bladeprofile 39 (most clearly shown in the right half of bit 10 in FIG. 4)may generally be divided into three regions conventionally labeled coneregion 24, shoulder region 25, and gage region 26. Cone region 24comprises the radially innermost region of bit 10 (e.g., cone region 24is the central most region of bit 10) and composite blade profile 39extending generally from bit axis 11 to shoulder region 25. As shown inFIG. 4, in most fixed cutter bits, cone region 24 is generally concave.Adjacent cone region 24 is shoulder (or the upturned curve) region 25.Thus, composite blade profile 39 of bit 10 includes one concaveregion-cone region 24, and one convex region-shoulder region 25. In mostfixed cutter bits, shoulder region 25 is generally convex. Movingradially outward, adjacent shoulder region 25 is the gage region 26which extends parallel to bit axis 11 at the outer radial periphery 23of composite blade profile 39. Outer radius 23 extends to and thereforedefines the full gage diameter of bit 10. Cone region 24 is defined by aradial distance along the x-axis measured from central axis 11. It isunderstood that the x-axis is perpendicular to central axis 11 andextends radially outward from central axis 11. Cone region 24 may bedefined by a percentage of outer radius 23 of bit 10. The actual radiusof cone region 24, measured from central axis 11, may vary from bit tobit depending on a variety of factors including without limitation, bitgeometry, bit type, location of one or more secondary blades, locationof back up cutting elements 50, or combinations thereof. The axiallylowermost point of convex shoulder region 25 and composite blade profile39 defines a blade profile nose 27. At blade profile nose 27, the slopeof a tangent line 27 a to convex shoulder region 25 and composite bladeprofile 39 is zero. Thus, as used herein, the term “blade profile nose”refers to the point along a convex region of a composite blade profileof a bit in rotated profile view at which the slope of a tangent to thecomposite blade profile is zero. For most fixed cutter bits (e.g., bit10), the composite blade profile includes only one convex shoulderregion (e.g., convex shoulder region 25), and only one blade profilenose (e.g., nose 27). Advantageously, by placing rolling cutters inareas of the bit experiencing the greatest wear, for example at theshoulder region 26 of a bit, the wear rate of the bit may be improved.

Further, in a particular embodiment, a bit may have cutting elementsplaced in a single set configuration with rolling cutters placed inareas of the bit experiencing the greatest wear. In another embodiment,a bit may have cutting elements placed in a plural set configuration,wherein at least one rolling cutter is placed in areas of the bitexperiencing the greatest wear.

In addition to varying the placement of rolling cutters, otherstrategies may be employed to enhance the life of a drill bit.Specifically, in one or more embodiments, the use of different chamfersizes depending on the radial location and/or type of cutting element(fixed or rotatable) may be utilized. For example, one design strategyis to use a set of rolling cutters that employ a first chamfer, and asecond set of non-rolling cutters that employ a second chamfer. In oneembodiment, the rolling cutters have a “small chamfer” while thenon-rolling cutters employ a “large chamfer,” but variations are withinthe scope of the present invention. In another embodiment, the rollingcutters have a “large chamfer” while the non-rolling cutters employ a“small” chamfer. In another embodiment, cutters (rolling or fixed) in aradially interior region of cutting profile may have a “large” chamferwhile the outer radial positions may be rolling cutters having a “small”chamfer. As used herein, the terms “small” and “large” are used asrelative terms, i.e., the “small chamfer” is simply smaller than the“large chamfer.”

FIGS. 5A and 5B depict an example “smaller chamfer” cutting element 1000comprised of a superabrasive, diamond table 1012 supported by a carbidesubstrate 1014. The interface 1016 between the PDC diamond table 1012and the substrate 1014 may be planar or non-planar, according to manyvarying designs for same as known in the art. Cutting element 1000 issubstantially cylindrical and symmetrical about longitudinal axis 1018,although such symmetry is not required and non-symmetrical cutters areknown in the art.

Cutting face 1020 of cutting element 1000, to be oriented on a bitfacing generally in the direction of bit rotation, extends substantiallytransversely to such direction, and to axis 1018. The surface 1022 ofthe central portion of cutting face 1020 is planar as shown, althoughconcave, convex, ridged or other substantially, but not exactly, planarsurfaces may be employed. A chamfer 1024 extends from the periphery ofsurface 1022 to cutting edge 1026 at the sidewall 1028 of diamond table1012. Chamfer 1024 and cutting edge 1026 may extend about the entireperiphery of table 1012, or only along a periphery portion to be locatedadjacent the formation to be cut.

Chamfer 1024 may comprise a 0.012 inch at 45° conventional chamfer, ormay lie at some other angle, as referenced with respect to the chamfer1124 of cutter 1110 described below. For conventional PDC cutters, aconventional chamfer size (radial width) and angle would be 0.012 inch(looking at and perpendicular to the cutting face of the diamond table)oriented at a 45° angle with respect to the longitudinal cutter axis,thus providing a larger radial width as measured on the chamfer surfaceitself. While 0.012 inch chamfer size is referenced as an example(within conventional tolerances), the present disclosure relates to theuse of multiple chamfer sizes.

FIGS. 6 through 8 depict an exemplary “larger chamfer” cutting element1110 comprised of a superabrasive, diamond table 1112 supported by acarbide substrate 1114.

The interface 1116 between the diamond table 1112 and the substrate 1114may be planar or non-planar, according to many varying designs for sameas known in the art (see especially FIGS. 7 and 8). Cutting element 1110is substantially cylindrical and symmetrical about longitudinal axis1118, although such symmetry is not required and non-symmetrical cuttersare known in the art.

Cutting face 1120 of cutting element 1110, to be oriented on a bitfacing generally in the direction of bit rotation, extends substantiallytransversely to such direction, and to axis 1118. The surface 1122 ofthe central portion of cutting face 1120 is planar as shown, althoughconcave, convex, ridged or other substantially, but not exactly, planarsurfaces may be employed. A chamfer 1124 extends from the periphery ofsurface 1122 to cutting edge 1126 at the sidewall 1128 of diamond table1112. Chamfer 1124 and cutting edge 1126 may extend about the entireperiphery of table 1112, or only along a periphery portion to be locatedadjacent the formation to be cut. Chamfer 1124 may comprise a surfaceoriented at 45° to axis 1118, of a width, measured looking at andperpendicular to the cutting face 1120, of 0.018 inches.

However, as mentioned above, the “small chamfer” and “large chamfer” maybe relative to one another, and chamfer sizes other than 0.012 and 0.018inches may certainly be used. In one or more embodiments, a firstchamfer size may fall within the range of 0.001 to about 0.010 inch(measured as previously described), with 0.006 to 0.008 inches being anexample sub-range. In one or more embodiments, a second chamfer size mayfall within the range of 0.008 to 0.020 inches, with 0.010 to about0.014 inches and 0.014 to 0.020 as being example sub-ranges. In one ormore embodiments, a third chamfer size may fall within a range of 0.020to 0.035 inches, and a fourth chamfer size may fall within a range of0.035 inch to 0.060 (or larger). Thus, the “small chamfer” and “largechamfer” may be selected from the above ranges (or sub-ranges), and the“small chamfer” may be, but does not have to be, selected from the firstsize range or second size range, for example. It is also within thescope of the present disclosure that the different chamfer sizes may beselected within the same size range (such as in FIGS. 5-8 above), solong as the sizes selected are themselves varied. Further, in oneembodiment, the smaller chamfer may have an upper limit of any of 0.018,0.016, 0.014, 0.012, or 0.010 inches, and the larger chamfer may have alower limit of any of 0.012, 0.014, 0.016, 0.018, 0.020, or 0.024.Further, it is also within the scope of the present disclosure that athird or intermediate chamfer size (or more) may also be used.

For either of the cutting element types, chamfer angles of about 10° toabout 80° to axis 1118 may be useful, with angles in the range of about30° to about 60° being used in particular embodiments. The effectiverake angle of a chamfer with respect to the formation may be altered bychanging the back rake of the cutter. Further, it is also within thescope of the present disclosure that one or more cutting elements mayincorporate a variable bevel, as described in U.S. Pat. No. 7,726,420,which is assigned to the present assignee and herein incorporated byreference in its entirety.

Specifically, embodiments disclosed herein include rolling cutters, ornon-rolling cutters, disposed in a nose and/or shoulder of the bit,having small bevel (or chamfer) size. In one or more other embodiments,the rolling or non-rolling cutters disposed in a nose and/or shoulder ofthe bit can have a large bevel (or chamfer). However, using a smallbevel on the rolling cutters in a shoulder area may provide a number ofadvantages. First, by employing a small bevel, there is a lower forcerequired to rotate the rolling cutter, which may enhance the rollingcutter life by allowing more even wear. In addition, much of the cuttingaction in directional drilling applications and other applicationsoccurs at the shoulder, and simply by the larger path drilled, cuttingelements in the shoulder tend to experience more wear than cuttingelements in radially interior locations (such as the cone). By having asmaller bevel in the shoulder, the rolling cutters have a higher diamondvolume, which allows the cutters to cut more effectively. Additionally,the rolling cutters wear in a different manner than conventional, fixedcutters. Specifically, the wear pattern observed effectively enlargesthe chamfer size by creating an even wear around the entirecircumference.

Conversely, by providing large bevel cutting elements (rolling ornon-rolling) adjacent the center, (such as in the cone and/or nose ofthe bit), better impact resistance and durability is provided to thosecutting elements, which is important around the center of the bit,particularly as these cutting elements tend to experience the highestdepth of cut. Moreover, it is believed that such an arrangement may helpto avoid bit slip, and torque spikes associated with bit slip.

Further, it is also within the scope of the present disclosure that thecutting elements within nose may have a distinct chamfer size ascompared to the cone and shoulder. For example, in one or moreembodiments, the nose may have an intermediate chamfer size. Further, itis also within the scope of the present disclosure that multiple chamfersizes may be used within a single zone (i.e., cone, nose, shoulder).

Additionally, as mentioned above, there is also a region of the cuttingprofile referred to as the gage. In one or more embodiments, the gageregion may incorporate any of rolling cutters having a “small” chamfer,rolling cutters having a “large chamfer”, non-rolling cutters having a“small” chamfer, or non-rolling cutters having a “large chamfer”(relative to radially interior cutting elements). In particularembodiments, the gage cutting element may have a large chamfer, or mayeven be a pre-flat, as that term is understood by those skilled in theart.

In one particular embodiment the effect of varying the bevel size on arolling cutter for a given formation and weight on bit combination wasanalyzed. In this embodiment, carthage marble, having a compressivestrength of 3,000 psi was used as an exemplary rock formation. Theweight on bit was set at 20,000 lbs. The cutting and side forces seen bytwo rolling cutters having different bevels was then determined usinganalysis software such as disclosed in U.S. Pat. No. 7,844,426, which isexpressly incorporated by reference in its entirety.

In this embodiment a “standard” bevel of 0.012 in. at 45 degrees wasanalyzed, as well as a “medium” bevel of 0.016 in. at 45 degrees. Theresults from the software are shown in FIGS. 9 and 10. As shown in FIG.9, the standard bevel (marked as 1802) has a higher cutting force thanthe medium bevel (shown at 1804). Similarly, in FIG. 10, the standardbevel (1902) has a higher side force than the medium bevel (1904). As aresult, the standard bevel is predicted to both penetrate deeper intothe formation (based on the higher cutting force) than the medium bevel.As a result, it is believed that having a smaller bevel size on therolling cutters than on the non-rolling cutters is advantageous in thisembodiment.

In selected embodiments, because cutters in the cone/nose area seehigher overall forces than the cutters in the shoulder/flank area,larger bevels are preferred in the cone/nose area, to provide increasedcutter durability in this area. Typical bevel size mix for cone/nose toshoulder/flank area should be 0.012″-0.030″ to 0.010″-0.025″. The Tablebelow provides representative groups of bevel size mixes (where therolling cutters are placed in the shoulder/flank, and non-rolling orrolling cutters are placed in the cone/nose). All bevels in the tableare at 45 degrees.

Cone/nose bevel Shoulder/Flank Example size bevel size Ex 1 0.010″0.006-0.010″ Ex 2 0.012″ 0.008-0.012″ Ex 3 0.016″ 0.010-0.016″ Ex 40.020″ 0.012-0.020″ Ex 5 0.025″ 0.016-0.025″

The table above is exemplary only, and other embodiments are within thescope of the present invention. Within the table, however, whenselecting a cone/nose bevel size, the shoulder/flank bevel size will beset smaller than the cone/nose.

Bits having a plurality of rolling cutters of the present disclosure mayinclude at least two rolling cutters, for example at least three, atleast 4, at least 6, at least 9, or at least 12 rolling cutters, withany remaining cutting elements being conventional fixed cuttingelements. In one or more embodiments, two or more primary blades maycontain one or more rolling cutters, for example each primary blade maycontain one or more rolling cutters. In one or more additionalembodiments, one or more secondary blades may also contain one or morerolling cutters, for example each secondary blade may contain one ormore rolling cutters. In one or more embodiments, all cutting elementsmay be rotatable.

Other Design Options

According to some embodiments, the extension height of cutting elementcutting faces (i.e., the upper surface of the cutting table of thecutting element) may vary. In an example embodiment, cutting faces ofprimary cutting elements may have a greater extension height than thecutting faces of backup cutting elements (i.e., “on-profile” primarycutting elements engage a greater depth of the formation than the backupcutting elements; and the backup cutting elements are “off-profile”). Asused herein, the term “off-profile” may be used to refer to a structureextending from the cutter-supporting surface (e.g., the cutting element,depth-of-cut limiter, etc.) that has an extension height less than theextension height of one or more other cutting elements that define theoutermost cutting profile of a given blade. As used herein, the term“extension height” is used to describe the distance a cutting faceextends from the cutter-supporting surface of the blade to which it isattached. In some example embodiments, one or more backup cutting facesmay have the same or a greater extension height than one or more primarycutting faces. Such variables may impact the properties of the bottomhole assembly, in particular the drill bit, which can affect thearrangement or positioning of the different types of cutting elements.For example, “on-profile” cutting elements may experience a greateramount of wear and load than “off-profile” cutting elements. Also,primary cutting elements may experience a greater amount of wear andload than backup cutting elements.

Referring to FIG. 11, a cutting structure profile of a bit according toone embodiment is shown. As shown in this embodiment, cutters 2600positioned on a blade 2602 may have side rake or back rake. Side rake isdefined as the angle between the cutting face 2605 and the radial planeof the bit (x-z plane). When viewed along the z-axis, a negative siderake results from counterclockwise rotation of the cutter 2600, and apositive side rake, from clockwise rotation. Back rake is defined as theangle subtended between the cutting face 2605 of the cutter 2600 and aline parallel to the longitudinal axis 2607 of the bit. In oneembodiment, a cutter may have a side rake ranging from 0 to ±45 degrees,for example ±5 to ±35 degrees, ±10 to ±35 degrees or ±15 to ±30 degrees.In a particular embodiment, the direction (positive or negative) of theside rake may be selected based on the cutter distribution, i.e.,whether the cutters are arranged in a forward or reverse spiralconfiguration. For example, in embodiments, if cutters are arranged in areverse spiral, positive side rake angles may be particularly desirable.Conversely, if cutters are arranged in a forward spiral, negative siderake angles may be particularly desirable.

In some embodiments, each rolling cutter placed in the nose and/orshoulder region of the bit may have a side rake ranging from 10 to 30degrees or −10 to −30 degrees. In other embodiments, each rolling cutterplaced in the nose and/or shoulder region of the bit may have a siderake ranging from 20 to 30 degrees or −20 to −30 degrees. In someembodiments, rolling cutters radially outside the shoulder, i.e., in thegage region, may range from 5 to 35 degrees or −5 to −35 degrees. Inmore particular embodiments, rolling cutters in the gage region maybe >5 degrees, >10 degrees, >15 degrees, >20 degrees, >25 degrees, >30degrees, and/or <10 degrees, <15 degrees, <20 degrees, <25, <30 degrees,<35 degrees, with any of such angles being positive or negative, and anyupper limit being used with any lower limit. Further, in someembodiments, cutters may be placed in the cone region of the bit mayhave a side rake of less than 20 degrees or ranging from 10 to 15degrees in more particular embodiments. In various embodiments, cuttersin the cone region may be either fixedly attached or may be rolling, butmay have such side rake range if fixed or rolling. It is specificallyunderstood that any of the side rake angles for any region may be usedin singly or in combination with any of the other ranges for otherregions. Further, in one or more embodiments, the fixed cutters may beoriented at a side rake that is less than the side rake of the rotatablecutting elements, such as at side rake angles of less than 10 degrees.

In another embodiment, a cutter may have a back rake ranging from about5 to 35 degrees. In a particular embodiment, the back rake angle of arolling cutter may be >5 degrees, >10 degrees, >15 degrees, >20degrees, >25 degrees, >30 degrees, and/or <10 degrees, <15 degrees, <20degrees, <25, <30 degrees, <35 degrees, with any upper limit being usedwith any lower limit. Such back rake angles may be used for rollingcutters in any of the cone, nose, shoulder or gage region of the bit,but in particular embodiments, a back rake of between 10 and 35 degrees(or 15 to 35 degrees or 20 to 30 degrees in more particular embodiments)may be particularly suitable for cutters in the nose and/or shoulderregion of the bit. A cutter may be positioned on a blade with a selectedback rake to assist in removing drill cuttings and increasing rate ofpenetration. A cutter disposed on a drill bit with side rake may beforced forward in a radial and tangential direction when the bitrotates. In some embodiments, because the radial direction may assistthe movement of a rotatable cutting element, such rotation may allowgreater drill cuttings removal and provide an improved rate ofpenetration. One of ordinary skill in the art may realize that any backrake and side rake combination may be used with the cutting elements ofthe present disclosure to enhance rotatability and/or improve drillingefficiency.

In one or more other embodiments, cutting elements may be disposed incutting tools that do not incorporate back rake and/or side rake. Whenthe cutting element is disposed on a drill bit with substantially zerodegrees of side rake and/or back rake, the cutting force may be randominstead of pointing in one general direction. The random forces maycause the cutting element to have a discontinuous rotating motion.Generally, such a discontinuous motion may not provide the mostefficient drilling condition, however, in certain embodiments, it may bebeneficial to allow substantially the entire cutting surface of theinsert to contact the formation in a relatively even manner. In such anembodiment, alternative inner rotatable cutting element and/or cuttingsurface designs may be used to further exploit the benefits of rotatablecutting elements. Further, in one or more other embodiments, a bevel orchamfer size, angle, or design may be selected to accommodate for a zeroback or side rake.

Exemplary Embodiments of Rolling Cutters

Rolling cutters of the present disclosure may include various types andsizes of rolling cutters. For example, rolling cutters may be formed insizes including, but not limited to, 9 mm, 13 mm, 16 mm, and 19 mm.Further, the type of rolling cutter is of no limitation to the presentdisclosure. Rather, it may be of any type and/or include any featuresuch as those described in U.S. Pat. No. 7,703,559, U.S. patentapplication Ser. Nos. 13/152,626, 61/479,183, 61/479,151, or 61/556,454,all of which are assigned to the present assignee and hereinincorporated by reference in their entirety. Exemplary embodiments ofrolling cutters are also described below; however, the types ofrotatable cutting elements that may be used with the present disclosureare not necessarily limited to those described below.

Referring now to FIGS. 12 and 13, a rotatable cutting element assemblyaccording to embodiments of the present disclosure is shown.Particularly, an exploded view of the cutting element is shown in FIG.12, including a rolling cutter 300, a retaining ring 320, and a sleeve330. The rolling cutter 300 has an axis of rotation A extendinglongitudinally therethrough, a cutting face 302, and a body 304extending axially downward from the cutting face 302. The body 304 hasan outer surface 306 and a circumferential groove 310 formed therein.Particularly, the circumferential groove 310 is formed on a shaft 308portion of the body 304 and extends a height axially along the shaft 308and around the circumference of the shaft 308. Further, a cutting edge303 is formed at the intersection of the cutting face 302 and the outersurface 306 of the rolling cutter 300. As shown, the cutting face 302and cutting edge 303 may be formed from a diamond or other ultra-hardmaterial table 305.

A cross-sectional view of the assembled cutting element is shown in FIG.13, wherein the rolling cutter 300 is partially disposed within thesleeve 330, and wherein the retaining ring 320 is disposed between therolling cutter 300 and the sleeve 330, within the circumferential groove310. Particularly, the shaft 308 portion of the rolling cutter 300 isdisposed within the sleeve 330. As shown, the portion of the rollingcutter 300 outside of the sleeve 330 has a first diameter X₁, and theshaft 308 has a second diameter X₂, wherein the first diameter X₁ islarger than the second diameter X₂. The sleeve 330 has a first innerdiameter Y ₁ and a second inner diameter Y ₂, wherein the second innerdiameter Y ₂ is larger than the first inner diameter Y ₁ and located ata lower axial position than the first inner diameter Y₁. The seconddiameter X₂ of the shaft 308 may be substantially equal to the firstinner diameter Y₁ of the sleeve, so that the shaft may fit within thesleeve 330. As used herein, a substantially equal diameter includes asufficient gap to allow the rolling cutter 300 to rotate within thesleeve 330. For example, the gap formed by difference between the shaftsecond diameter X₂ and the sleeve first inner diameter Y₁ may range fromabout 0.001 to 0.030 inches. Further, the sleeve 330 may have an outerdiameter Y₃. As shown, the portion of the rolling cutter 300 remainingoutside the sleeve 330 may have a first diameter X₁ that issubstantially equal to the sleeve outer diameter Y₃, such that theassembled cutting element has a cylindrical shape. However, according toother embodiments, the rolling cutter first diameter X₁ be greater thanor less than the sleeve outer diameter Y₃.

The sleeve 330 may have varying inner diameter sizes in addition to thefirst inner diameter Y₁ and the second inner diameter Y₂. For example,as shown in FIG. 5, a top end 331 of the sleeve 330 may have a graduallyincreasing inner diameter from the first inner diameter Y₁. According tosome embodiments, a sleeve may also have an inner diameter smaller thanthe second inner diameter located axially downward from the second innerdiameter and from the circumferential groove of an assembled cuttingelement. In such embodiments, a retaining ring may protrude from thecircumferential groove into the space provided by the second innerdiameter.

The circumferential groove 310 formed around the outer surface of therolling cutter body may be axially positioned along the shaft 308 sothat the circumferential groove 320 abuts the transition 332 between thesleeve first inner diameter Y₁ and second inner diameter Y₂. In otherwords, the circumferential groove 320 and the sleeve second innerdiameter Y₂ both extend a distance in the same axial direction from thesame axial position along the assembled cutting element. For example, asshown in FIG. 5, the circumferential groove has a first sidewall 311, asecond side wall 312, and a base surface 313. The circumferential groove310 extends a height axially along the shaft 308 from the first sidewall311 to the second sidewall 312. The first sidewall 311 is locatedaxially at the same position along the assembled cutting element as thetransition 332 to the second inner diameter Y₂, thereby aligning thecircumferential groove 310 with the transition 332 to the second innerdiameter Y2 to create an interface surface 314 adjacent to the retainingring 320. The retaining ring 320 may rotate around the interface surface314, and the rolling cutter 300 may rotate within the sleeve 330, suchthat the transition surface 332 and first sidewall 311 maintain theinterface surface 314 with the retaining ring 320.

As assembled, the cutting element has a retaining ring 320 disposed inthe circumferential groove 310, wherein the retaining ring 320 extendsat least around the entire circumference of the shaft 308. For example,in the embodiment shown in FIGS. 12 and 13, the retaining ring 320 mayextend greater than 1.5 times around the circumference of the shaft 308.As shown in FIG. 13, the retaining ring 320 protrudes from thecircumferential groove 310 to contact the second inner diameter Y₂ ofthe sleeve 330, thereby retaining the rolling cutter 300 within thesleeve 330. However, according to other embodiments, the retaining ringmay protrude from the circumferential groove without contacting thesecond inner diameter to retain the rolling cutter within the sleeve.

However, the present disclosure is not limited to the rolling cuttertype illustrated in FIGS. 12 and 13, but instead, as mentioned above,any type of rolling cutter may be used on the bits and tools of thepresent disclosure.

In various embodiments, the cutting face of the inner rotatable cuttingelement may include an ultra hard layer that may be comprised of apolycrystalline diamond table, a thermally stable diamond layer (i.e.,having a thermal stability greater than that of conventionalpolycrystalline diamond, 750° C.), or other ultra hard layer such as acubic boron nitride layer.

As known in the art, thermally stable diamond may be formed in variousmanners. A typical polycrystalline diamond layer includes individualdiamond “crystals” that are interconnected. The individual diamondcrystals thus form a lattice structure. A metal catalyst, such ascobalt, may be used to promote recrystallization of the diamondparticles and formation of the lattice structure. Thus, cobalt particlesare typically found within the interstitial spaces in the diamondlattice structure. Cobalt has a significantly different coefficient ofthermal expansion as compared to diamond. Therefore, upon heating of adiamond table, the cobalt and the diamond lattice will expand atdifferent rates, causing cracks to form in the lattice structure andresulting in deterioration of the diamond table.

To obviate this problem, strong acids may be used to “leach” the cobaltfrom a polycrystalline diamond lattice structure (either a thin volumeor entire tablet) to at least reduce the damage experienced from heatingdiamond-cobalt composite at different rates upon heating. Examples of“leaching” processes can be found, for example, in U.S. Pat. Nos.4,288,248 and 4,104,344. Briefly, a strong acid, typically hydrofluoricacid or combinations of several strong acids may be used to treat thediamond table, removing at least a portion of the co-catalyst from thePDC composite. Suitable acids include nitric acid, hydrofluoric acid,hydrochloric acid, sulfuric acid, phosphoric acid, or perchloric acid,or combinations of these acids. In addition, caustics, such as sodiumhydroxide and potassium hydroxide, have been used to the carbideindustry to digest metallic elements from carbide composites. Inaddition, other acidic and basic leaching agents may be used as desired.Those having ordinary skill in the art will appreciate that the molarityof the leaching agent may be adjusted depending on the time desired toleach, concerns about hazards, etc.

By leaching out the cobalt, thermally stable polycrystalline (TSP)diamond may be formed. In certain embodiments, only a select portion ofa diamond composite is leached, in order to gain thermal stabilitywithout losing impact resistance. As used herein, the term TSP includesboth of the above (i.e., partially and completely leached) compounds.Interstitial volumes remaining after leaching may be reduced by eitherfurthering consolidation or by filling the volume with a secondarymaterial, such by processes known in the art and described in U.S. Pat.No. 5,127,923, which is herein incorporated by reference in itsentirety.

Alternatively, TSP may be formed by forming the diamond layer in a pressusing a binder other than cobalt, one such as silicon, which has acoefficient of thermal expansion more similar to that of diamond thancobalt has. During the manufacturing process, a large portion, 80 to 100volume percent, of the silicon reacts with the diamond lattice to formsilicon carbide which also has a thermal expansion similar to diamond.Upon heating, any remaining silicon, silicon carbide, and the diamondlattice will expand at more similar rates as compared to rates ofexpansion for cobalt and diamond, resulting in a more thermally stablelayer. PDC cutters having a TSP cutting layer have relatively low wearrates, even as cutter temperatures reach 1200° C. However, one ofordinary skill in the art would recognize that a thermally stablediamond layer may be formed by other methods known in the art,including, for example, by altering processing conditions in theformation of the diamond layer.

The substrate on which the cutting face is disposed may be formed of avariety of hard or ultra hard particles. In one embodiment, thesubstrate may be formed from a suitable material such as tungstencarbide, tantalum carbide, or titanium carbide. Additionally, variousbinding metals may be included in the substrate, such as cobalt, nickel,iron, metal alloys, or mixtures thereof. In the substrate, the metalcarbide grains are supported within the metallic binder, such as cobalt.Additionally, the substrate may be formed of a sintered tungsten carbidecomposite structure. It is well known that various metal carbidecompositions and binders may be used, in addition to tungsten carbideand cobalt. Thus, references to the use of tungsten carbide and cobaltare for illustrative purposes only, and no limitation on the typesubstrate or binder used is intended. In another embodiment, thesubstrate may also be formed from a diamond ultra hard material such aspolycrystalline diamond and thermally stable diamond. While theillustrated embodiments show the cutting face and substrate as twodistinct pieces, one of skill in the art should appreciate that it iswithin the scope of the present disclosure the cutting face andsubstrate are integral, identical compositions. In such an embodiment,it may be preferable to have a single diamond composite forming thecutting face and substrate or distinct layers.

The cutting elements of the present disclosure may be incorporated invarious types of downhole cutting tools, including for example, ascutters in fixed cutter bits or as inserts in roller cone bits, reamers,hole benders, or any other tool that may be used to drill earthenformations. Cutting tools having the cutting elements of the presentdisclosure may include a single rotatable cutting element with theremaining cutting elements being conventional cutting elements, allcutting elements being rotatable, or any combination therebetween ofrotatable and conventional cutting elements.

The cutting elements of the present disclosure may be attached to ormounted on a drill bit by a variety of mechanisms, including but notlimited to conventional attachment or brazing techniques in a cutterpocket, as well as by mechanical means. It is also within the scope ofthe present disclosure that in some embodiments, an inner rotatablecutting element may be mounted on the bit directly such that the bitbody acts as the outer support element, i.e., by inserting the innerrotatable cutting element into a hole that may be subsequently blockedto retain the inner rotatable cutting element within.

Advantageously, embodiments disclosed herein may provide for at leastone of the following. Cutting elements that include a rotatable cuttingportion may avoid the high temperatures generated by typical fixedcutters. Because the cutting surface of prior art cutting elements isconstantly contacting formation, heat may build-up that may causefailure of the cutting element due to fracture. Embodiments inaccordance with the present disclosure may avoid this heat build-up asthe edge contacting the formation changes. The lower temperatures at theedge of the cutting elements may decrease fracture potential, therebyextending the functional life of the cutting element. By decreasing thethermal and mechanical load experienced by the cutting surface of thecutting element, cutting element life may be increased, thereby allowingmore efficient drilling.

Further, rotation of a rotatable portion of the cutting element mayallow a cutting surface to cut formation using the entire outer edge ofthe cutting surface, rather than the same section of the outer edge, asprovided by the prior art. The entire edge of the cutting element maycontact the formation, generating more uniform cutting element edgewear, thereby preventing formation of a local wear flat area. Becausethe edge wear is more uniform, the cutting element may not wear asquickly, thereby having a longer downhole life, and thus increasing theoverall efficiency of the drilling operation.

Additionally, because the edge of the cutting element contacting theformation changes as the rotatable cutting portion of the cuttingelement rotates, the cutting edge may remain sharp. The sharp cuttingedge may increase the rate of penetration while drilling formation,thereby increasing the efficiency of the drilling operation. Further, asthe rotatable portion of the cutting element rotates, a hydraulic forcemay be applied to the cutting surface to cool and clean the surface ofthe cutting element.

Some embodiments may protect the cutting surface of a cutting elementfrom side impact forces, thereby preventing premature cutting elementfracture and subsequent failure. Still other embodiments may use adiamond table cutting surface as a bearing surface to reduce frictionand provide extended wear life. As wear life of the cutting elementembodiments increase, the potential of cutting element failuredecreases. As such, a longer effective cutting element life may providea higher rate of penetration, and ultimately result in a more efficientdrilling operation.

Advantageously, therefore, embodiments disclosed herein may provide forimproved drilling performance, in directional and non-directionalapplications, and/or may increase cutter life. Also advantageously, byproviding larger sized bevels in the cone region, when the bit issubject to directional drilling (under sliding conditions), there can bea reduction in cutter breakage. This is due to the weight transfer fromthe drilling string to the bit which can be intermittent and hard tocontrol, thus, could accidently damage the cone/nose cutters having asmaller bevel size due to sudden depth of cut increase.

Also, by using a larger bevel in the cone/nose area, the DOC (depth ofcut) could be limited by the larger bevel in the cone/nose area toprevent accidental deeper bite into the rock which creates high torqueand vibration during transitional drilling. This is especially importantwhen the bit is used in directional drilling where tool face control ismore important than the rate of penetration.

Also advantageously, by providing the smaller bevel on theshoulder/flank area there may be less contact area as compared to alarger bevel if the ROP is the same, thus further reducing the torsionalspikes. Also advantageously, with rolling cutters installed in theshoulder/flank area, the smaller bevel (comparing to the cutters in thecone/nose area) could also have less side/cutting force as compared to alarger bevel, enabling better rotation due to less friction within therolling cutter assembly, leading to enhanced durability.

While the above describes a situation where the rolling cutters have afirst chamfer and the non-rolling cutters have a second chamfer, it isalso contemplated that mixed chamfers may be used on the same type ofcutter. In other words, it is expressly within the scope of the presentinvention that the rolling cutters may be mixed smaller and largerchamfers. One other option is to provide a depth limiter on thenon-rolling cutters, instead of a large bevel.

Although only a few example embodiments have been described in detailabove, those skilled in the art will readily appreciate that manymodifications are possible in the example embodiments without materiallydeparting from this invention. Accordingly, all such modifications areintended to be included within the scope of this disclosure as definedin the following claims. In the claims, means-plus-function clauses areintended to cover the structures described herein as performing therecited function and not only structural equivalents, but alsoequivalent structures. Thus, although a nail and a screw may not bestructural equivalents in that a nail employs a cylindrical surface tosecure wooden parts together, whereas a screw employs a helical surface,in the environment of fastening wooden parts, a nail and a screw may beequivalent structures. It is the express intention of the applicant notto invoke 35 U.S.C. §112, paragraph 6 for any limitations of any of theclaims herein, except for those in which the claim expressly uses thewords ‘means for’ together with an associated function.

What is claimed is:
 1. A cutting tool comprising: a tool body having aplurality of blades extending radially therefrom; a plurality ofrotatable cutting elements, having a first chamfer mounted on at leastone of the plurality of blades; and a plurality of non-rotatable cuttingelements, having a second, distinct chamfer mounted on at least one ofthe plurality of blades.
 2. The cutting tool of claim 1, wherein thefirst chamfer is smaller than the second chamfer.
 3. The cutting tool ofclaim 2, wherein the first chamfer is no more than 0.014 inches.
 4. Thecutting tool of claim 3, wherein the first chamfer is no more than 0.012inches.
 5. The cutting tool of claim 1, wherein the first chamfer islarger than the second chamfer.
 6. The cutting tool of claim 1, whereinthe plurality of rotatable cutting elements are located in a shoulderregion of the blade.
 7. The cutting tool of claim 1, where at least onerotatable cutting element is disposed in a nose region of the blade. 8.The cutting tool of claim 7, wherein the at least one rotatable cuttingelement in the nose region has a third chamfer.
 9. The cutting tool ofclaim 1, wherein the plurality of non-rotatable cutting elements arelocated in a cone region of the blade.
 10. The cutting tool of claim 1,where at least one non-rotatable cutting element is disposed in a noseregion of the blade.
 11. The cutting tool of claim 10, wherein the atleast one non-rotatable cutting element in the nose region has a thirdchamfer.
 12. The cutting tool of claim 1, wherein the second chamfer isat least 0.014 inches.
 13. The cutting tool of claim 12, wherein thesecond chamfer is at least 0.016 inches.
 14. A cutting tool comprising:a tool body having a plurality of blades extending radially therefrom; aplurality of rotatable cutting elements, wherein the plurality ofrotatable cutting elements have at least two differing chamfer sizesbased on their positioning along the plurality of blades.
 15. Thecutting tool of claim 14, further comprising a plurality ofnon-rotatable cutting elements
 16. The cutting tool of claim 15, whereinthe plurality of non-rotatable cutting element have a chamfer distinctfrom at least one rotatable cutting element.
 17. The cutting tool ofclaim 14, wherein at least one rotatable cutting element located in thecone has a larger chamfer than at least one rotatable cutting elementlocated in the shoulder.
 18. The cutting tool of claim 14, wherein atleast one rotatable cutting elements located in the cone has a smallerchamfer than at least one rotatable cutting element located in theshoulder.
 19. The cutting tool of claim 17, wherein the at least onerotatable cutting element in the nose region has a chamfer in betweenthe chamfer size of the at least one rotatable cutting element locatedand in the cone and the at least one rotatable cutting element locatedin the nose.